The subject matter of the present invention is a method for the preparation of glycol esters of organosilanes, in which at least two organosilicon groupings are linked together by a glycol or polyglycol moiety in the manner of an ester. The compounds are suitable as hydraulic fluids, heat carrier oils or system intermediates.
It is known, for example, from German Offenlegungsschrift No. 2,445,552 that a number of organosilane esters of mono- or polyfunctional organic hydroxy compounds in hydraulic oil formulations are a good guarantee of reliability and safety in hydraulically operated mechanical systems against very often life-threatening failures. This is due mostly to their water-binding properties, their compatibility with rubber and their heat-stability. They therefore constitute a considerable advance over the prior art.
The desire to employ these substances practically, however, has hitherto been thwarted by the fact that the production of these compounds on a large technical scale presents serious problems.
The above-mentioned compounds are essentially those of the formula ##STR1## wherein R is a glycol substituent of the general formula ##STR2## R'=RO-- or a substituent from the group R"; R"=alkyl (C.sub.1 -C.sub.20), branched if desired, alkenyl, cycloalkyl or aryl;
R'"=H or CH.sub.3 ; PA1 n=1-12 PA1 p=0-10 (average degree of condensation),
and in some cases their branching products if R'=RO--.
For lack of any more practical method of procedure, the preparation of these very much sought-after products had to be performed in accordance with the above-mentioned patents, by partially esterifying a chlorosilane of the formula ##STR3## wherein X represents either chlorine or R' of the meaning given above, and R" has the same meaning as above, in the presence of an amine (pyridine, for example) intercepting hydrogen chloride, with a glycol of the formula ##STR4## wherein R'" and n have the meaning given above, and then continuing and completing the esterification, also in the presence of an amine, with a glycol ether of the formula ##STR5## wherein R'", R"" and q have the meaning given above. In some cases the two glycols could be used in reverse order. Towards the end of the reaction, the large and unusable amount of amine hydrochloride which necessarily had to form as a by-product had to be separated, and the large amount of solvent that had to be used on account of the great production of salt had to be removed by evaporation.
Lastly, then, the surplus of salt still dissolved in the product had to be removed by a complex refinement because it cannot be tolerated in hydraulic applications. The yields of this burdensome method of preparation in no case exceeded 70%. The disadvantages of this method of preparation--the only one available heretofore--are obvious.
To avoid the difficulties involved in the process described above, attempts have also been made to arrive at the desired products by the catalyzed or uncatalyzed transesterification of organosilane esters of the general formula ##STR6## wherein Y represents a substituent R' in the meaning given above, or a substituent --OR"", and R"" also has the meaning given above, with glycols or glycol monoethers. These reactions, however, were very slow and incomplete. But it was regularly found that these processes of transesterification do not lead to the desired products but instead yield products of different composition. Especially the low alkoxy group is quite stubbornly retained, making the products unsuitable for hydraulic applications because their excessively low Gilpin vapor lock temperature impairs their ability to perform. These discouraging results suggested the conclusion that the transesterification approach is not promising, on account of the above-described disadvantages.
The problem therefore existed of finding a method of preparing the above-named glycol esters which does not have the burdensome disadvantages described above.